Background: The degenerative tissue changes in temporomandibular joint (TMJ) disorders may affect articular cartilage and adjacent connective tissue responses. Different types of matrix metalloproteinases (MMPs) are involved in these changes. Diseases of the TMJ are more prevalent in women than in men and the reasons for this sexual dimorphism remain unclear. However, potential role of relaxin in the aetiology of TMD, has been proposed recently. The relaxin is an insulin-like hormone produced in the ovaries during pregnancy, and also has multi-functional factor in broad range of target tissues including several non-reproductive organs also in males. Major effects of relaxin are extracellular matrix remodelling, collagen degradation and up-regulation of MMPs. Degradation of fibrocartilaginous tissues of the TMJ by induction of MMP family along with relaxin has been reported. The aim of this study was to evaluate the level of hormone relaxin in synovial fluids of patients with TMJ internal derangements with or without osteoarthritis (OA) and joint effusion (JE).

Patients and methods: 28 patients (26 female and 2 male) with TMJ internal derangements with/without OA and JE on MRI were included. Synovial fluid of 28 joints obtained by arthrocentesis for therapeutic reasons was analyzed by ELISA for relaxin. The patients were subdivided according to whether they have OA and JE or not. Chi square and Wilcoxon-signed-rank test were used for statistical analysis ( p < 0.05).

Results: Of 20 (75%) joints had OA, while 13 (47%) joints showed JE on MR imaging. The mean relaxin levels was 0.82 ± 0.54 pg/ml (ranging from 0.7 to 2.67). The increases in means of relaxin was statistically significant in joints with effusion ( p = 0.030), while no statistical significance was found between relaxin and OA ( p > 0.05).

Conclusion: Increased level of relaxin may influence the expression of JE and may play important role in the physiopathology of TMD. This may also explain the high women prevalence.

Key words: TMD; relaxin; synovial fluid